The Australian Department of Foreign Affairs attempted to verify the reports but said it was “very difficult to do so,” Agence France-Presse reported.
The man, not named in reports, is believed to be from south-west Sydney and married with children, according to the Sun Herald.
“Due to the extremely dangerous security situation, consular assistance is no longer available within Syria or Iraq,” a foreign ministry spokesman said in a statement.
The news come after reports that ISIS chief Abu Bakr al-Baghdadi had been seriously injured following a U.S.-led air strike on a militant convoy, Al Arabiya News reported citing tribal sources.
The U.S. could not confirm or deny that he was part of the gathering that was targeted near the northern Iraqi city of Mosul.
The Australian government passed a law criminalizing travel to terror hotspots in October, in response to fears about the flow of foreign fighters to the Middle East.
Authorities suspect almost 70 Australians are believed to have already made the journey, with another 100 supporting them with recruitment and funding from home.
Of those who have travelled, an estimated 20 militants who fought with terrorist groups in the region have also returned to Australia, while a further 73 people have had their passports cancelled to prevent them joining ISIS, Canberra said.
Fifteen Australians, including two suicide bombers, are already thought to have died fighting in Syria and Iraq, Australia's then intelligence chief David Irvine said in late August.
The country raised its terror threat level in September and carried out extensive counter-terrorism raids in Sydney and Brisbane, with Attorney-General George Brandis warning last week that Australians should brace for more large-scale operations.
These developments follow the death of ISIS’ most senior Australian recruit, Mohamed Ali Baryalei, who was reportedly killed two weeks ago during fighting in Syria.
The Herald reported that another ISIS fighter from Sydney, Abu Noor al-Kurdi, was also killed with Baryalei.